Joint timing recovery for multiple signal channels

ABSTRACT

A spatial diversity receiver and method for determining a multichannel combined symbol timing marker that identifies an energy concentration for a combination of channel delay spreads in order to reduce the complexity of equalization. The receiver includes two or more receiver chains having spatially diverse antennas; a multichannel combined timer; and a multichannel combined equalizer for receiving wireless signals through two or more signal channels. The multichannel combined timer combines energies corresponding to the channel impulse response coefficients for all the channels for determining a series of multichannel combined metrics having associated index cursors, and then determines the multichannel combined symbol timing marker from the index cursor for the largest of the metrics. The symbol timing marker synchronizes the received symbols issued to the equalizer jointly to the energy concentration for the delay spreads combined for all the channels.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to symbol timing recovery and moreparticularly to an apparatus and method for recovering a common symboltiming marker for multiple channel signals received with multipleantennas.

2. Description of the Prior Art

When a signal is transmitted over a channel with multiple propagationpaths with different delays (multipath channels), the received signal isa linearly dispersed (smeared) version of the transmitted signal.Equalization and spatial diversity are used in existing systems forreducing the distorting effects of multipath. Spatial diversity requiresmultiple antennas for receiving a signal through multiple signalchannels. Equalization uses an equalizer to recover the originaltransmitted signal from its dispersed version at the receiver, in thepresence of additive noise.

The equalizer requires an estimate of the impulse response of thechannel through which the transmission took place. In packet-basedsystems that require fast startup, the channel estimate is typicallyobtained by processing a known training sequence, such as a preamble,midamble or a synch word. The channel impulse response estimate isobtained as a series of samples or “coefficients” that represent themultipath delay spread profile of the channel during a particularpacket.

Several equalizer structures exist in the art. A maximum likelihoodsequence estimate (MLSE) equalizer provides optimum symbol detection.Unfortunately, the number of trellis states in an MLSE equalizerincreases exponentially with the number of impulse responsecoefficients. Unless the packet time is accurately known and the delayspread is narrow, the complexity of the MLSE equalizer can beprohibitive.

Two other equalizer types commonly used today are the decision feedbackequalization (DFE) equalizer and delayed decision feedback sequenceestimation (DDFSE) equalizer. The DFE equalizer uses a feedforwardfilter and the DDFSE equalizer uses a Viterbi sequence estimator.However, the DFE and DDFSE equalizers are also prohibitively complexunless time is accurately known and delay spread is small because thenumber of taps in the feedforward filter and the number of states in theViterbi sequence estimator increase with the number of coefficients ofthe channel impulse response.

Ariyavisitakul in U.S. Pat. No. 5,809,086 entitled “Intelligent TimingRecovery for a Broadband Adaptive Equalizer” incorporated herein byreference presents a technique for reducing the complexity of DFE orDDFSE equalizers. Unfortunately, the symbol timing recovery systemspresented by Ariyavisitakul are operable only for a single signalchannel. Anvari et al. in U.S. Pat. No. 6,130,909 shows a multichannelsystem having equalization. However, the system shown by Anvari et al.and all others so far as is known, would be expected to suffer from poorperformance if any one of the multiple channels had a lowsignal-to-noise. There remains a need for a symbol timing recoverysystem for reducing equalizer complexity in a multichannel system.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amultichannel method and apparatus for determining a multichannelcombined symbol timing marker that identifies an energy concentrationfor a combination of channel delay spreads in a combination of signalchannels in order to reduce the complexity of equalization.

Briefly, in a preferred embodiment, a multichannel signal receiver ofthe present invention includes two or more receiver chains; amultichannel combined timer including a multichannel combiner and ametric comparator; and a multichannel combined equalizer for receivingwireless signals through two or more signal channels. The equalizer hasa predetermined span for equalizing the channels.

The receiver chains include spatially diverse antennas, signalprocessing circuitry, and channel estimators. The antennas and thesignal processing circuitry receive the wireless channel signals andprovide receiver chain signals. The channel estimators use the receiverchain signals for determining channel impulse response coefficients foreach signal channel. The multichannel combiner combines energiescorresponding to the channel coefficients from all the channels fordetermining a series of multichannel combined metrics having associatedindex cursors. The metric comparator determines the largest of themetrics and issues a multichannel combined symbol timing marker for thecorresponding cursor. The symbol timing marker identifies the locationin time of the energy concentration for the delay spread for thecombination of the signal channels. The equalizer equalizes thecombination of the channel signals jointly synchronized by the symboltiming marker for providing equalized symbols.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodimentswhich are illustrated in the various figures.

IN THE DRAWINGS

FIG. 1 is a block diagram of a multichannel signal receiver of thepresent invention;

FIG. 2 is a block diagram showing multipath signals received throughmultiple signal channels by multiple antennas in the receiver of FIG. 1;

FIG. 3 is a block diagram of an MLSE embodiment of a multichannelcombiner of the receiver of FIG. 1;

FIGS. 4A and 4B are charts showing channel impulse response coefficientsfor exemplary first and second channel impulse response coefficients,respectively;

FIG. 4C is a chart showing a multichannel combined symbol timing markerof the present invention for the exemplary first and second channelimpulse response coefficients of FIGS. 4A and 4B;

FIG. 5 is a block diagram of a DFE embodiment of a multichannel combinerof the receiver of FIG. 1;

FIG. 6 is a block diagram of a DDFSE embodiment of a multichannelcombiner of the receiver of FIG. 1; and

FIGS. 7A-D are charts showing phases τ₀-τ₃, respectively, for exemplarymultichannel combined metrics for the receiver of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a multichannel signal receiver of thepresent invention referred to by the general reference number 10. Thereceiver 10 includes two or more receiver chains 1, 2 through L. Asdescribed herein, structural elements of the receiver chains 1, 2through L are referenced with subscripts “1”, “2” through “L”,respectively. It should be noted that the present invention can be usedwith any number of channels and receiver chains equal to or greater thantwo.

The receiver chains 1, 2 through L include antennas A₁, A₂ throughA_(L), respectively, having different spatial positions (spatialdiversity). Referring to FIG. 2, a transmitter 12 transmits a wirelesstransmitted signal that passes through channels CH₁, CH₂ through CH_(L)to be received as wireless channel signals S_(CH1), S_(CH2) throughS_(CHL) by the antennas A₁, A₂ through A_(L), respectively. In general,each of the channel signals S_(CH1), S_(CH2) through S_(CHL) is composedof several signals traveling different geometric paths (multipath) dueto reflections. Because the antennas A₁, A₂ through A_(L) have differentspatial positions, the multipath fading experienced by one of theantennas A₁, A₂ through A_(L) will not necessarily be experienced by theother antennas A₁, A₂ through A_(L).

Returning to FIG. 1, the receiver chains 1, 2 through L include analogcircuitry, denoted G₁, G₂ through G_(L), analog-to-digital converters,denoted A/D₁, A/D₂ through A/D_(L), and digital circuitry, denoted g₁,g₂ through g_(L). The antennas A₁, A₂ through A_(L) convert the RFwireless signals S_(CH1), S_(CH2) through S_(CHL) into RF conductedsignals and pass the RF conducted signals to the analog circuitry G₁, G₂through G_(L). The analog circuitry G₁, G₂ through G_(L) amplifies,filters and frequency downconverts the RF conducted output signals tointermediate signals and pass the intermediate signals to theanalog-to-digital converters A/D₁, A/D₂ through A/D_(L). Theanalog-to-digital converters A/D₁, A/D₂ through A/D_(L) convert theintermediate signals from an analog format to a digital format and passthe digital format signals to the digital circuitry g₁, g₂ throughg_(L). Preferably, there are several analog-to-digital converters A/D₁,A/D₂ through A/D_(L) operating in parallel sampled at two or more offsetphases τ for providing parallel digital signals at the phases τ. Thedigital circuitry g₁, g₂ through g_(L) amplifies, level shifts, filtersand/or frequency converts the digital signals for providing receiverchain signals r_(1,n)(τ), r_(2,n)(τ) through r_(L,n)(τ), respectively,as shown in an equation 1, below. $\begin{matrix}{{{r_{l,n}(\tau)} = {{\sum\limits_{k = {- K_{1}}}^{K_{2}}\quad{x_{n - k}{h_{l,k}(\tau)}}} + \eta_{l,n}}},{k = {{- K_{1}}\quad{to}\quad K_{2}}}} & (1)\end{matrix}$

In the equation 1, the r_(l,n)(τ)=r_(l)(nT+τ) is the receiver chainsignal for the lth receiver chain at a receiver chain index ncorresponding to a time nT+τ where the τ denotes the phase and the T isthe symbol period. The x_(n−k)=x_(m) is the mth symbol in thetransmitted signal from the transmitter 12 (FIG. 2). Theh_(l,k)(τ)=h_(l,k)(kT+τ) are the channel impulse response coefficientsfor the lth channel (CH₁, CH₂ through CH_(L)) at channel impulseresponse indexes k where k takes on values from a first channel impulseresponse index −K₁ to a last channel impulse index +K₂. The channelsCH₁, CH₂ through CH_(L) are assumed to have channel impulse responsecoefficients of zero, h_(l,k)(τ)=0, for k less than the first channelindex −K₁ or greater than the last channel index +K₂. The η_(l,n) is thenoise on the lth receiver chain signal at the nth receiver chain index.

The receiver 10 includes a multichannel combined timer 18 including amultichannel combiner 20 and a metric comparator 22. The multichannelcombiner 20 blends the channel impulse response coefficients from allreceiver chains 1, 2 through L for determining a series of multichannelcombined metrics and the metric comparator 22 determines a multichannelcombined symbol timing marker S_(C) (FIG. 4C) as described in thedetailed descriptions below from the largest of the multichannelcombined metrics.

The receiver 10 also includes an equalizer 23, channel estimators 24 ₁,24 ₂ through 24 _(L), data buffers 26 ₁, 26 ₂ through 26 _(L), channelbuffers 28 ₁, 28 ₂ through 28 _(L); and optional receiver chain noiseestimators 34 ₁, 34 ₂ through 34 _(L). The channel estimators 24 ₁, 24 ₂through 24 _(L) estimate sets of the channel impulse responsecoefficients h_(l,k)(τ), h_(2,k)(τ) through h_(L,k)(τ) according to theequation 1 by correlating the receiver chain signals r_(1,n)(τ),r_(2,n)(τ) through r_(L,n)(τ) against a known training sequence for thetransmitted symbols x_(m). The data buffers 26 ₁, 26 ₂ through 26 _(L)use the symbol timing marker S_(C) (FIG. 4C) to synchronize the receiverchain signals r_(1,n)(τ), r_(2,n)(τ) through r_(L,n)(τ) to the incomingsymbols for providing synchronized receiver chain signals DATA₁, DATA₂through DATA_(L), respectively, to the equalizer 23.

The channel buffers 28 ₁, 28 ₂ through 28 _(L) provide synchronizedchannel signals CHAN₁, CHAN₂ through CHAN_(L), respectively, which are asubset of the channel coefficients h_(1,k)(τ), h_(2,k)(τ) throughh_(L,k)(τ), k=−K₁ to K₂. The length of each of the CHAN_(1-L) is equalto an equalizer span W. The first index k of the equalizer span W isidentified by the symbol timing marker S_(C). The equalizer 23 uses thesynchronized channel signals CHAN₁, CHAN₂ through CHAN_(L) for thesymbol timing marker S_(C) (FIG. 4C) and the equalizer index span W forequalizing the synchronized receiver chain signals DATA₁, DATA₂ throughDATA_(L) in order to provide equalized symbols. For example, when thesymbol timing marker S_(C) corresponds to a channel index k=10 and theequalizer span W is 6, the equalizer 23 uses the channel coefficientsh_(1,k)(τ), h_(2,k)(τ) through h_(L,k)(τ) for the impulse responseindexes 10, 11, 12, 13, 14 and 15 with the DATA_(1-L) signalscorresponding to the marker S_(C) for providing the equalized symbols.

For optimum performance, the noise estimators 34 ₁, 34 ₂ through 34 _(L)determine receiver chain noise levels p₁, p₂ through p_(L)(corresponding to η_(l,n), in the equation 1) for the receiver chainsignals r_(1,n)(τ), r_(2,n)(τ) through r_(L,n)(τ), respectively. Thenoise levels p₁, p₂ through p_(L) can be determined from a receivedsignal strength indication (RSSI) measurement or by using a firstestimate of the symbol timing marker S_(C). The noise levels p₁, p₂through p_(L) can also be determined in an iterative approach using theequation 1 from the symbols in the receiver chain signals r_(1,n)(τ),r_(2,n)(τ) through r_(L,n)(τ). In the iterative approach either thesymbol timing marker S_(C) or the noises levels p₁, p₂ through p_(L) areestimated first. Then the estimate of the symbol timing marker S_(C) (orthe noise levels p₁, p₂ through p_(L)) is used to determining the noiselevels p₁, p₂ through p_(L) (or symbol timing marker S_(C)) and thedeterminations of the noise levels p₁, p₂ through p_(L) (or symboltiming marker S_(C)) are used to refine the estimate of the symboltiming marker S_(C) (or noise levels p₁, p₂ through p_(L)) and so on.

The noise levels p₁, p₂ through p_(L) are used in the multichannelcombiner 20 for scaling the energies of the channel impulse responsesh_(1,k)(τ), h_(2,k)(τ) through h_(L,k)(τ) by receiver chain scalefactors 1/p₁, 1/p₂ through 1/p_(L), respectively. However, empiricalresults show that this scaling is not necessary for some systems andthat good results may be obtained using equally weighted channel impulseresponse energies |h_(1,k)(τ)|², |h_(2,k)(τ)|² through |h_(L,k)(τ)|².The scale factors may or may not be a constant and may or may not be thesame for all channel impulse response energies |h_(1,k)(τ)|²,|h_(2,k)(τ)|² through |h_(L,k)(τ)|² depending upon the system.

The channel impulse response coefficients h_(1,k)(τ), h_(2,k)(τ) throughh_(L,k)(τ) and optionally the noise levels p₁, p₂ through p_(L) or otherscale factors are received by the multichannel combiner 20. Themultichannel combiner 20 combines the energies of the channel impulseresponse coefficients h_(l,k)(τ), h_(2,k)(τ) through h_(L,k)(τ) forpredetermined channel indexes k into multichannel combined metricshaving associated index cursors c (and phases τ). The range of thechannel indexes k and the combining algorithms (EQS. 2-4) depend uponthe type of equalizer 23. Successive multichannel combined metrics arecomputed for successive cursors c starting at the cursor c at the firstchannel index (−K₁) and ending with the cursor c at the equalizer span Wless than the last channel index (K₂−W). The metric comparator 22determines the largest of the multichannel combined metrics anddesignates the cursor c (and the phase τ) associated with the largestmultichannel combined metric as the symbol timing marker S_(C) (FIG.4C).

There are several types of equalizers that can be used for the equalizer23. Three of these types of the equalizer 23 are known in general termsas a maximum likelihood sequence estimator (MLSE) equalizer, a decisionfeedback equalization (DFE) equalizer, and a decision feedback sequenceestimation (DDFSE) equalizer. The multichannel combiner 20 hasembodiments 20A, 20B and 20C for use with the MLSE, DFE and DDFSEembodiments, respectively, of the equalizer 23.

FIG. 3 is a block diagram of an MLSE embodiment of the multichannelcombiner 20 referred to with the reference designator 20A. The MLSEmultichannel combiner 20A computes a series of multichannel combinedmetrics, denoted as α(c, τ), according to an equation 2, below.$\begin{matrix}{{{\alpha\left( {c,\tau} \right)} = {\sum\limits_{l}\quad{\frac{1}{p_{l}}{\sum\limits_{k = c}^{c + W}\quad{{h_{l,k}(\tau)}}^{2}}}}},{c = {- K_{1}}},\ldots\quad,{K_{2} - W}} & (2)\end{matrix}$

As shown in the equation 2, the multichannel combiner 20A determines theseries of multichannel combined metrics α(c, τ) by combining the channel(impulse) response energies lip, 1/p₁|h_(1,k)(τ)|², 1/p₂|h_(2,k)(τ)|²through 1/p_(L)|h_(L,k)(τ)|² for index k ranges equal to the equalizerindex span W starting at index cursors c for the series of the indexcursors c, respectively. The series of the cursors c takes on indexesfrom the first channel index −K₁ to the span W less than the lastchannel index +K₂. The metric comparator 22 determines the largest ofthe multichannel combined metrics α(c, τ) and then uses the cursor c andphase τ (FIGS. 7A-D) of the argument (c, τ) of the largest of themultichannel combined metrics α(c, τ) for the symbol timing markerS_(C).

The multichannel combiner 20A in a preferred embodiment includes amultichannel sliding span combiner 42 and functional elements, denotedas squarers 45 ₁, 45 ₂ through 45 _(L) for deriving channel responseenergies |h_(1,k)(τ)|², |h_(2,k)(τ)|² through |h_(L,k)(τ)|² from thechannel impulse response coefficients h_(1,k)(τ), h_(2,k)(τ) throughh_(L,k)(τ), respectively. Optionally, the MLSE multichannel combiner 20Aalso includes functional elements, denoted as scalers 46 ₁, 46 ₂ through46 _(L) for scaling the channel response energies |h_(1,k)(τ)|²,|h_(2,k)(τ)|² through |h_(L,k)(τ)|² by the receiver chain scale factors1/p₁, 1/p₂ through 1/p_(L). The multichannel sliding span combiner 42adds the index range of the channel response energies 1/p₁|h_(1,k)(τ)|²,1/p₂|h_(2,k)(τ)|² through 1/p_(L)|h_(L,k)(τ)|² for the equalizer indexspan W for the successive cursors c from −K₁ to +K₂−W for providing themultichannel combined metrics α(c, τ).

FIGS. 4A and 4B illustrate an exemplary case having first and secondchannel impulse response coefficients h_(1,k)(τ) and h_(2,k)(τ),respectively, for the channel index k from a first index 0 (−K₁) to alast index 22 (+K₂) and a phase τ=τ₀. The dotted lines 48 ₁ and 48 ₂represent envelopes of the channel impulse response coefficientsh_(1,k)(τ₀) and h_(2,k)(τ₀), respectively, and the vertical solid lines49 ₁ and 49 ₂ represent the channel impulse response coefficientsh_(1,k)(τ) and h_(2,k)(τ), respectively, at the channel indexes k. Thespan W of the equalizer 23 is shown as six of the channel indexes k. Thecursor c has a range of channel indexes k from −K₁ to +K₂−W.

In the exemplary case, it can be seen by inspection that the channelimpulse response coefficients h_(1,k)(τ₀) have an equalizer spanWconcentration of energy indicated by a symbol timing marker S₁corresponding to the cursor c that in turn corresponds to the channelindex k=9 (moving S₁ by one channel index k in either direction willdecrease the sum of the first channel response energies |h_(l,k)(τ)|² inthe span W). Similarly, for the second channel response coefficientsh_(2,k)(τ₀) it can be seen by inspection that the symbol timing markerS₂ for the equalizer span W concentration of energy corresponds to thecursor c that corresponds to the channel index k=15 (moving S₂ by onechannel index k in either direction will decrease the sum of the secondchannel response energies |h_(2,k)(τ₀)|² in the span W).

FIG. 4C shows the results of calculations in the exemplary caseaccording to the equation 2 for the multichannel combined metrics α(c,τ) for the MLSE embodiment 20A (FIG. 3) for the cursors c from −K₁ to+K₂−W. The vertical bars 50 represent the energy levels of themultichannel combined metrics α(c, τ) for the cursors c from −K₁ to +K₂−W. The multichannel symbol timing marker S_(C) indicates the cursor ccorresponding to the channel index k=10 for the largest of themultichannel combined metrics α(c, τ) for the equalizer span Wconcentration of energy for the multichannel signal receiver 10 of thepresent invention. It should be noted that the joint symbol timingmarker S_(C) of the present invention is not equal to either of theindividual markers S₁ or S₂, or to their average. More generally, thereis no way to derive the joint symbol timing marker Sc from the knowledgeof S₁ and S₂ alone, other than using the joint timing recovery methodsof the present invention.

FIG. 5 is a block diagram of an DFE embodiment of the multichannelcombiner 20 referred to with the reference designator 20B. The DFEmultichannel combiner 20B computes a series of multichannel combinedmetrics, denoted as β(c, τ), according to an equation 3, below.$\begin{matrix}{{{\beta\left( {c,\tau} \right)} = \frac{\sum\limits_{l}\quad{\frac{1}{p_{l}}{{h_{l,c}(\tau)}}^{2}}}{{\sum\limits_{l}\left( \quad{\frac{1}{p_{l}}{\sum\limits_{k = {- K_{1}}}^{c - 1}{{h_{l,k}(\tau)}}^{2}}} \right)} + N_{0}}},{c = {- K_{1}}},\ldots\quad,{K_{2} - W}} & (3)\end{matrix}$

As shown in the equation 3, the multichannel combiner 20B determines theseries of multichannel combined metrics β(c, τ) by inversely scaling(deemphasizing) a sum of the channel response energies1/p₁|h_(1,c)(τ)|², 1/p₂|h_(2,c)(τ)|₂ through 1/p_(L)|h_(L,c)(τ)|²corresponding to a particular one of the index cursors c by a sum of aninitial precursor term N₀ plus a sum of the channel response energies1/p₁|h_(1,k)(τ)|², 1/p₂|h_(2,k)(τ)|² through 1/p_(L)|h_(L,k)(τ)|² forthe index k ranges from the first index −K₁ to one less than theparticular index cursor c, for the series of the index cursors c,respectively. The series of the cursors c takes on indexes from thefirst channel index −K₁ to the equalizer span W less than the lastchannel index +K₂. When the optional noise scale factors 1/p₁, 1/p₂through 1/p_(L) are used, the initial precursor term N₀ may be set toone. When the optional noise scale factors 1/p₁, 1/p₂ through 1/p_(L)are not used, the initial precursor term N₀ should be set to somefunction of the noise levels p₁, p₂ through p_(L), preferably the lowestof the noise levels p₁, p₂ through p_(L).

For example when the current cursor c=−K₁, the multichannel combinedmetric β(c, τ) is the sum of the channel response energies 1/p₁|h_(1,−K)₁ (τ)|²+1/p₂|h_(2,−K) ₁ (τ)|² through +1p_(L)|h_(L,−K) ₁ (τ)|² dividedby 1/N₀. When the cursor c=−K₁+1, the multichannel combined metric β(c,τ) is the sum of the channel response energies 1/p₁|h_(1,−K) ₁₊₁(τ)|²+1/p₂|h_(2,−K) ₁ ₊₁(τ)|² through +1/p_(L)|h_(L,−K) ₁ ₊₁(τ)|²divided by the sum of the initial precursor term N₀ plus the channelresponse energies 1/p₁|h_(1,−K) ₁ ₊₁(τ)|²+1/p₂|h_(2,−K) ₁ ₊₁(τ)|²through +1/p_(L)|h_(L,−K) ₁ ₊₁(τ)|². When the cursor c=−K₁+2, themultichannel combined metric β(c, τ) is the sum of the channel responseenergies 1/p₁|h_(1,−K) _(i) ₊₂(τ)|²+1/p₂|h_(2,−K) ₁ ₊₂(τ)|² through+1/p_(L)|h_(L,−K) ₁ ₊₂(τ)|² divided by the sum of the initial precursorterm N₀ plus 1/p₁|h_(1,−K) ₁ ₊₁(τ)|²+1/p₂|h_(2,−K) ₁ ₊₁(τ)|² through+1/p_(L)|h_(L,−K) ₁ ₊₁(τ)|² plus 1/p₁|h_(1,−K) ₁ ₊₂(τ)|²+1/p₂|h_(2,−K) ₁₊₂(τ)|² through +1/p_(L)|h_(L,−K) ₁ ₊₂(τ)|². The example may becontinued on in the same way for the cursor c from −K₁+2 to +K₂−W.

In a preferred embodiment the DFE multichannel combiner 20B includes amultichannel deemphasizer 52 and a multichannel precursor calculator 54.The DFE multichannel combiner 20B also includes the fuinctional squarers45 ₁, 45 ₂ through 45 _(L) and optionally the functional scalers 46 ₁,46 ₂ through 46 _(L) operating as described above. The multichanneldeemphasizer 52 includes a multichannel sliding combiner 56 and a scaler58.

The multichannel precursor calculator 54 sums the initial precursor termN₀ and the channel response energies 1/p₁|h_(1,k)(τ)|²,1/p₂|h_(2,k)(τ)|² through 1/p_(L)|h_(L,k)(τ)|² over a range of thechannel indexes k from −K₁ to the channel index k one less than thecursor c for the series of cursors c from −K₁ to K₂−W for determining aseries of precursor deemphasis coefficients. When the cursor c=−K₁, theprecursor deemphasis coefficient is N₀. The multichannel slidingcombiner 56 sums the channel response energies 1/p₁|h_(1,c)(τ)|²,2/p₂|h_(2,c)(τ)|² through 1/p_(L)|h_(L,c)(τ)|² for the cursor c forproviding a series of multichannel single index sums for the series ofcursors c from −K₁ to K₂−W. The scaler 58 deemphasizes (inverselyscales) the series of multichannel single index sums by the series ofprecursor deemphasis coefficients, respectively, for providing theseries of multichannel combined metrics β(c, τ). The metric comparator22 determines the largest one of the multichannel combined metrics β(c,τ) and then uses the argument (c, τ) of the largest of the multichannelcombined metrics β(c, τ) for the symbol timing marker S_(C).

FIG. 6 is a block diagram of an DDFSE embodiment of the multichannelcombiner 20 referred to with the reference designator 20C. The DDFSEmultichannel combiner 20C computes a series of multichannel combinedmetrics, denoted as χ(c, τ), according to an equation 4, below.$\begin{matrix}{{{\chi\left( {c,\tau} \right)} = \frac{\sum\limits_{l}\quad{\frac{1}{p_{l}}{\sum\limits_{k = c}^{c + W}\quad{{h_{l,k}(\tau)}}^{2}}}}{{\sum\limits_{l}\left( \quad{\frac{1}{p_{l}}{\sum\limits_{k = {- K_{1}}}^{c - 1}\quad{{h_{l,k}(\tau)}}^{2}}} \right)} + N_{0}}},{c = {- K_{1}}},\ldots\quad,{K_{2} - W}} & (4)\end{matrix}$

As shown in the equation 4, the multichannel combiner determines theseries of multichannel combined metrics χ(c, τ) by inversely scaling(deemphasizing) a sum of the channel (impulse) response energies1/p₁|h_(1,k)(τ)|², 1/p₂|h_(2,k)(τ)|² through 1/p_(L)|h_(L,k)(τ)|² forindex k ranges equal to the equalizer span W starting at particularindex cursors c with a sum of the initial precursor term N₀ plus a sumof the channel response energies 1/p₁|h_(1,k)(τ)|², 1p₂|h_(2,k)(τ)|²through 1/p_(L)|h_(L,k)(τ)|² for the index k ranges from the first index−K₁ to one less than the particular index cursors c. The series of thecursors c takes on indexes from the first channel index −K₁ to theequalizer span W less than the last channel index +K₂.

In a preferred embodiment the DDFSE multichannel combiner 20C includes amultichannel span deemphasizer 62; and the multichannel precursorcalculator 54, the functional squarers 45 ₁, 45 ₂ through 45 _(L), andoptionally the functional scalers 46 ₁, 46 ₂ through 46 _(L) operatingas described above. The multichannel span deemphasizer 62 includes themultichannel sliding span combiner 42 and the scaler 58 operating asdescribed above using the precursor deemphasis coefficients and thechannel response energies 1/p₁|h_(1,k)(τ)|², 1/p₂|h_(2,k)(τ)|² through1p_(L)|h_(L,k)(τ)|² for providing the series of channel combined metricsχ(c, τ). The metric comparator 22 determines the largest of themultichannel combined metrics χ(c, τ) and then uses the argument (c, τ)of the largest of the multichannel combined χ(c, τ) for the symboltiming marker S_(C).

FIGS. 7A, B, C, and D illustrate the phases τ of the channel index k atphase τ₀, phase τ₁, phase τ₂, and phase τ₃, respectively, themultichannel combined metrics α(c, τ), β(c, τ) or χ(c, τ). An envelopeof the multichannel combined metrics α(c, τ), β(c, τ) or χ(c, τ) betweenthe channel indexes k=6 and k=7 is shown as a dotted line 64 _(C). Thephases τ for more than one sample per symbol time period may be used forproviding for providing phased channel impulse response indexes k, τ.Where the phases τ are used, the multichannel combiner 20 computesphased multichannel combined metrics for each of the cursors c for eachof the phases τ. The metric comparator 22 determines the largest of thephased multichannel combined metrics and determines the symbol timingindex S_(C) from the associated cursor c and the phase τ of the largestphased multichannel combined metric.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter having read the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alterations and/modifications as fall within the true spirit and scope of theinvention.

1. A wireless signal receiver, comprising: two or more receiver chainshaving spatially diverse antennas for receiving a transmitted signal andproviding two or more receiver chain signals, respectively; two or morechannel estimators using said two or more receiver chain signals forestimating two or more sets of channel impulse response coefficients,respectively; and a multichannel combined timer using said two or moresets of said channel coefficients for determining a multichannelcombined symbol timing marker for synchronizing received symbols jointlyfor said two of more receiver chain signals.
 2. The receiver of claim 1,further comprising: an equalizer for jointly equalizing saidsynchronized received symbols for said two of more receiver chainsignals for providing equalized symbols for said transmitted signal. 3.The receiver of claim 1, wherein: the multichannel combined timerincludes a multichannel combiner for combining channel response energiescorresponding to said channel coefficients, respectively, in said two ormore sets for index ranges of said channel coefficients into a series ofmultichannel combined metrics having a corresponding series of indexcursors, said multichannel combined metrics used for identifying one ofsaid index cursors as said symbol timing marker.
 4. The receiver ofclaim 3, wherein: the multichannel combined timer further includes ametric comparator for determining said symbol timing marker as a one ofsaid index cursors associated with a largest one of said multichannelcombined metrics.
 5. The receiver of claim 3, wherein: the multichannelcombiner includes scalers for weighting said channel response energiesof said two or more sets of said channel coefficients with two or morescale factors, respectively, for providing scaled said channel responseenergies, the multichannel combiner combining said scaled channelresponse energies for determining said multichannel combined metrics. 6.The receiver of claim 5, further including: two or more noise estimatorsfor determining two or more noise levels from said two or more receiverchain signals, respectively; wherein said scale factors are inverselydependent on said noise levels, respectively.
 7. The receiver of claim3, wherein: said channel coefficients have associated impulse responseindexes from a first index to a last index for profiling delay spreadsfor two or more signal channels for said transmitted signal received bysaid two or more receiver chains, respectively; and said index cursorscorrespond to said impulse response indexes in a cursor range from saidfirst index to an equalizer index span less than said last index.
 8. Thereceiver of claim 7, wherein: the multichannel combiner determines saidseries of said multichannel combined metrics by combining said channelresponse energies for said impulse response indexes in said index rangesequal to said equalizer index span starting at said index cursors forsaid series of said index cursors, respectively.
 9. The receiver ofclaim 7, wherein: the multichannel combiner determines said series ofsaid multichannel combined metrics by inversely scaling a sum of saidchannel response energies corresponding to a particular one of saidindex cursors by a sum of an initial precursor term plus a sum of saidchannel response energies at said impulse response indexes for saidindex ranges from said first index to one less than said particularindex cursor for said series of said index cursors, respectively. 10.The receiver of claim 7, wherein: the multichannel combiner determinessaid series of multichannel combined metrics by inversely scaling a sumof said channel response energies for said impulse response indexes forsaid index ranges equal to said equalizer index span starting atparticular said index cursors in said series of said index cursors by asum of an initial precursor term plus a sum of said channel responseenergies at said impulse response indexes for said index ranges fromsaid first index to one less than said particular index cursors for saidseries of said index cursors, respectively.
 11. The receiver of claim 7,wherein: said impulse response indexes have at least two phases; the twoor more channel estimators provide each of said two or more sets of saidchannel coefficients at each of said least two phases for providingphased said channel coefficients; the multichannel combiner combinessaid channel response energies for said two or more sets of said phasedchannel coefficients for determining phased said multichannel combinedmetrics; and the metric comparator issues said symbol timing markercorresponding to a one of said index cursors associated with a largestone of said phased multichannel combined metrics.
 12. A method forreceiving a wireless signal, comprising: receiving a transmitted signalin two or more receiver chains having spatially diverse antennas forproviding two or more receiver chain signals, respectively; estimatingtwo or more sets of channel impulse response coefficients from said twoor more receiver chain signals, respectively; and determining amultichannel combined symbol timing marker from said two or more sets ofsaid channel coefficients for synchronizing received symbols jointly forsaid two of more receiver chain signals.
 13. The method of claim 12,further comprising: equalizing said synchronized received symbolsjointly for said two of more receiver chain signals for providingequalized symbols for said transmitted signal.
 14. The method of claim12, wherein: determining said multichannel combined symbol timing markerincludes combining channel response energies corresponding to saidchannel coefficients, respectively, in said two or more sets for indexranges of said channel coefficients into a series of multichannelcombined metrics having a corresponding series of index cursors fordesignating equalizer index spans of said channel coefficients, saidmultichannel combined metrics used for identifying one of said indexcursors as said symbol timing marker.
 15. The method of claim 14,wherein: determining said multichannel combined symbol timing markerincludes determining a largest one of said multichannel combined metricsand using a one of said index cursors associated with said largest oneof said multichannel combined metrics as said symbol timing marker. 16.The method of claim 14, wherein: combining said channel responseenergies includes weighting said channel response energies of said twoor more sets of said channel coefficients with two or more scalefactors, respectively, for providing scaled said channel responseenergies; and combining said scaled channel response energies fordetermining said multichannel combined metrics.
 17. The method of claim16, further comprising: determining two or more noise levels for saidtwo or more receiver chain signals, respectively; and calculating saidscale factors as inversely dependent on said noise levels, respectively.18. The method of claim 14, wherein: said channel coefficients haveassociated impulse response indexes from a first index to a last indexfor profiling delay spreads for two or more signal channels for saidtransmitted signal received by said two or more receiver chains,respectively; and said index cursors correspond to said impulse responseindexes in a cursor range from said first index to an equalizer indexspan less than said last index.
 19. The method of claim 18, wherein:combining said channel response energies includes determining saidseries of said multichannel combined metrics by combining channelresponse energies for said impulse response indexes in said index rangesequal to said equalizer index span starting at said index cursors forsaid series of said index cursors, respectively.
 20. The method of claim18, wherein: combining said channel response energies includesdetermining said series of said multichannel combined metrics bydeemphasizing a sum of said channel response energies corresponding to aparticular one of said index cursors by a sum of an initial precursorterm plus a sum of said channel response energies at said impulseresponse indexes for said index ranges from said first index to one lessthan said particular index cursor for said series of said index cursors,respectively.
 21. The method of claim 18, wherein: combining saidchannel response energies includes determining said series ofmultichannel combined metrics by deemphasizing a sum of said channelresponse energies for said impulse response indexes for said indexranges equal to said equalizer index span starting at particular saidindex cursors in said series of said index cursors by a sum of aninitial precursor term plus a sum of said channel response energies atsaid impulse response indexes for said index ranges from said firstindex to one less than said particular index cursors for said series ofsaid index cursors, respectively.
 22. The method of claim 18, wherein:said impulse response indexes have at least two phases; estimating saidtwo or more sets of said channel impulse response coefficients includesestimating said two or more sets of said channel coefficients at each ofsaid least two phases for providing phased said channel coefficients;combining said channel response energies includes combining said channelresponse energies for said two or more sets of said phased channelcoefficients for determining phased said multichannel combined metrics;and determining a multichannel combined symbol timing marker includesdetermining said symbol timing marker corresponding to a one of saidcursors associated with a largest one of said phased multichannelcombined metrics.